Effect of refeeding dietary containing different protein and lipid levels on growth performance, body composition, digestive enzyme activities and metabolic related gene expression of grass carp (Ctenopharyngodon idellus) after overwinter starvation

Fish often suffered starvation in the natural process of overwintering. After a long period of overwintering starvation, the actual demand of nutrients in refeeding diets for fish may be different from the appropriate demand level in normal culture environment. To investigate the effects of refeeding dietary containing different protein and lipid levels on the growth performance, body composition, digestive enzyme activities and metabolic related gene expression of grass carp (Ctenopharyngodon idellus) after overwintering starvation. The grass carp with an initial body weight of 133.05 +/- 2.88 g was fed 8 different protein and lipid levels of diets using a two-factor analysis (4 x 2) design, including 25%, 28%, 31%, 34% four crude protein levels and 4%, 8% crude lipid levels was tested for 56 days. The results showed that the diet containing 31% protein and 8% lipid significantly increased the final weight, weight gain rate, visceral ratio, intestinal ratio of grass carp after overwintering starvation and significantly decreased the feed conversion rate and hepatosomatic index compared to those fed the lower protein and lipid treatments (P < .05). With the increasing of diet protein levels, protein efficiency and protein deposition rates well as lipid deposition rate increased significantly and then decreased. The increasing of diet lipid level significantly increased the deposition of protein and lipid then promoted the utilization of diets (P < .05), the whole body crude protein and muscle crude lipid were significantly increased by 31% protein in diets, the diet containing 8% lipid significantly increased the whole body crude lipid, whole body crude ash and muscle crude lipid (P < .05). 31% protein in diet significantly decreased the content of triglyceride in serum, and the interaction of protein and lipid in diet significantly decreased the content of glucose and total cholesterol in serum (P < .05). The contents of hepatopancreas related digestive enzymes (protease, lipase and amylase) were significantly increased by 31% protein and 8% lipid (P < .05), and the repairment of hepatopancreas and intestinal tissue structure was promoted compared to those control groups. Dietary 31% protein levels and 8% lipid levels significantly increased protein and lipid deposition rates through influenced the gene expression of gldh, s6k, igf-i, tor in muscle and acc, fas in hepatopancreas (P < .05). According to the comprehensive analysis, it is recommended that refeeding diet containing 30.32%-30.41% protein and 8% lipid after overwintering starvation could significantly promote the growth performance, feed utilization, promote protein and lipid deposition and promote digestive system repair of grass carp. This study focused on the refeeding dietary contains approximate protein requirement of grass carp after overwinter starvation under two different lipid levels using practical feed formula and these results provide grass carp feed industry with very valuable information.